<script>
  var xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function() {
    console.log(xhr.readyState);
  };
  console.log(xhr.readyState);
  xhr.open('GET', 'test.php');
  xhr.send();
</script>
<p>
  <a href="file:///C:/Users/rise/Desktop/%E9%A6%96%E9%A1%B5/default/10.html">返回</a>
</p>